Non-volatile memories can still preserve the stored data when power is off, which enables them to be widely used in various types of electronic devices. One-time programmable memory (OTP) is one of the commonly used non-volatile memories, which uses memory units having intersected word lines and bit lines to store logic information, wherein a common memory unit has fuse, anti-fuse, and charge capturing devices (e.g., Floating Gate Avalanche-injection Field Effect Transistor). One-time programmable memory is generally non-repeatedly programmable.
For fuse type of OTP and anti-fuse type of OTP, a high voltage is required to break down insulating layer of capacitor. High power consumption loss will occur during the breakdown. Moreover, since the breakdown voltage is high, the power consumption of OTP is relatively large. Further, with the size of device scaling down proportionally, OTP which is based on oxide layer (i.e., insulating layer) breakdown effect will be subject to the problem of soft breakdown (since the thickness of oxide layer becomes thinner, the probability of occurring soft breakdown is greater).
FIG. 1 shows a schematic structural view of OTP unit of a split structure in the prior art. The OTP unit realizes the programming of OTP through the breakdown of gate oxide dielectric layer formed on a substrate. As shown in FIG. 1, the gate oxide dielectric layer comprises a first gate oxide dielectric layer 11 having a thickness of D1 and a second gate oxide dielectric layer 12 having a thickness of D2, wherein D2 is bigger than D1; each of the first gate oxide dielectric layer 11 and the second gate oxide dielectric layer 12 is formed thereon with a gate electrode, i.e., a gate electrode 13 and a gate electrode 14 respectively. The gate electrode 13 is correspondingly located above the first gate oxide dielectric layer 11, and the gate electrode 14 is correspondingly located above the second gate oxide dielectric layer 12. In this embodiment, the gate electrodes are each made of polysilicon. Since the thickness D1 of the first gate oxide dielectric layer 11 is smaller than the thickness D2 of the second gate oxide dielectric layer 12, when the gate electrodes 13 and 14 are simultaneously biased with a voltage, electric flux-lines are concentrated at an adjoining area of the first gate oxide dielectric layer 11 and the second gate oxide dielectric layer 12, making field intensity increase locally and making this area most vulnerable to breakdown. The adjoining area of the first gate oxide dielectric layer 11 and the second gate oxide dielectric layer 12 is the programming area of the OTP; when be programmed, breakdown points will arise in this area. Therefore, this structure can effectively lower programming voltage of fuse type of OTP and anti-fuse type of OTP.
However, the following problems exist with the OTP unit shown in FIG. 1.
(1) since the OTP is based on gate oxide dielectric layer breakdown and the gate oxide dielectric layer is relatively dense, the breakdown voltage will not be lowered too much; besides, the magnitude of programming voltage mainly depends on the thickness of the gate oxide dielectric layer; therefore, this solution still can not satisfy the requirement of low programming voltage;
(2) the gate oxide dielectric layer is formed above a substrate for forming active elements; therefore, the OTP unit is also formed in a front-end structure, which is typically integrated with the manufacture process of other active devices; thus, the thickness of the gate oxide dielectric layer is constrained by the structural design of other active devices, and the thickness of the gate oxide dielectric layer of OTP can also not designed flexibly.
(3) when a process node below 32 nm is developed for integrated circuit elements, a high-k dielectric will be commonly used instead of gate oxide dielectric layer; the gate oxide dielectric layer of the OTP unit shown in FIG. 1 will also be replaced by a high-k dielectric layer, which will lead to increase of leakage current, thus increasing power consumption of OTP unit.